This invention relates to a series of devices that can be easily applied to conventional vacuum spark advance (V.S.A.) motors of existing cars or new cars to limit the vacuum spark advance normally produced by engine intake suctions under certain driving conditions. It relates particularly to a device which changes a limit on the movement of the V.S.A. motor operating element in response to changes in engine speed. It can be adjusted to be responsive to different engine speeds corresponding to different speed limits imposed by authorities.
The conventional vacuum spark advance motors of most existing cars normally produce about one-half inch of travel at high intake suction, such as more than 12 to 15 inches of mercury (Hg) below atmosphere. This amount of travel may amount to about 15.degree. spark advance (more than the governor spark advance at many engine speeds).
This amount of spark advance at high intake suction (such as may be produced at level cruise at 50-70 m.p.h.), produces high combustion temperatures in the engine cylinders and improved mileage. However, high combustion temperatures tend to increase the amount of nitrous oxides (NO.sub.x) and therefore contribute undesirable exhaust emissions.
In an attempt to remedy this problem of undesirable NO.sub.x emissions, the prior art has disconnected the vacuum spark advance at all engine speeds or below a selected engine or road speed. However, such disconnection substantially reduces the engine efficiency and fuel economy.
Recent reports indicate that NO.sub.x is not as important a source of pollutant as was previously thought. Fuel consumption is becoming more important because of the present and the projected future fuel shortage and the adverse effect of foreign oil purchases on our balance of trade.